Laser power control arrangements in electro-optical readers

Abstract

Laser power control arrangements interrupt power to a laser used in electro-optical readers upon detection of an over-power condition not conforming to preestablished standards to meet prevalent safety standards.

1 . A laser power control arrangement in an electro-optical reader for reading indicia by directing a laser beam from a laser through a window supported by a housing to the indicia to be read, the arrangement comprising: 
 a) a scanner for sweeping the laser beam over a scan angle larger than the window between overscan regions located within the housing and away from the window;    b) an over-power circuit for detecting an over-power condition in which an output power of the laser beam exceeds a preestablished threshold, the over-power circuit including an over-power component at one of the overscan regions for enabling detection of the output power of the laser beam; and    c) a control circuit for deenergizing the laser upon detection of the over-power condition.    
   
   
       2 . The arrangement of  claim 1 , wherein the over-power component is a sensor for detecting the output power of the laser beam incident on the sensor, and for generating an over-power signal having a magnitude indicative of the output power of the laser beam.  
   
   
       3 . The arrangement of  claim 2 , wherein the sensor is an auxiliary photodetector spaced remotely from a main photodetector operative for detecting light scattered off the indicia to be read.  
   
   
       4 . The arrangement of  claim 1 , wherein the over-power component is a target for reflecting the laser beam incident on the target to a main photodetector operative for detecting light scattered off the indicia to be read, the main photodetector being operative for generating an over-power signal having a magnitude indicative of the output power of the laser beam when the laser beam is incident on the target.  
   
   
       5 . The arrangement of  claim 4 , wherein the target include areas of different light reflectivity.  
   
   
       6 . The arrangement of  claim 5 , wherein the target is a label affixed to said one overscan region, the areas of different light reflectivity being printed on the label.  
   
   
       7 . The arrangement of  claim 5 , wherein the target includes markings molded into said one overscan region.  
   
   
       8 . The arrangement of  claim 1 , wherein the over-power circuit is operative for generating an over-power signal having a magnitude indicative of the output power of the laser beam, for comparing the magnitude of the over-power signal with a reference value, and for generating a control signal when the magnitude of the over-power signal exceeds the reference value.  
   
   
       9 . The arrangement of  claim 8 , wherein the over-power circuit includes a differentiator for differentiating the over-power signal to obtain a differentiated signal having peaks, and a comparator for comparing the peaks to the reference value and for generating the control signal when the peaks exceed the reference value.  
   
   
       10 . The arrangement of  claim 8 , wherein the control circuit includes a switch electrically connected between a power source and the laser, and a controller for opening the switch upon generation of the control signal.  
   
   
       11 . A laser safety method during operating an electro-optical reader for reading indicia by directing a laser beam from a laser through a window supported by a housing to the indicia to be read, the method comprising the steps of: 
 a) sweeping the laser beam over a scan angle larger than the window between overscan regions located within the housing and away from the window;    b) detecting an over-power condition in which an output power of the laser beam exceeds a preestablished threshold, including the step of mounting an over-power component for enabling detection of the output power of the laser beam at one of the overscan regions; and    c) deenergizing the laser upon detection of the over-power condition.    
   
   
       12 . The method of  claim 11 , wherein the mounting step is performed by mounting a sensor for detecting the output power of the laser beam incident on the sensor, and for generating an over-power signal having a magnitude indicative of the output power of the laser beam.  
   
   
       13 . The method of  claim 12 , wherein the step of mounting the sensor is performed by remotely positioning the sensor away from a main photodetector operative for detecting light scattered off the indicia.  
   
   
       14 . The method of  claim 11 , wherein the mounting step is performed by mounting a target for reflecting the laser beam incident on the target to a main photodetector operative for detecting light scattered off the indicia, the main photodetector being operative for generating an over-power signal having a magnitude indicative of the output power of the laser beam.  
   
   
       15 . The method of  claim 14 , and the step of constituting the target of areas of different light reflectivity.  
   
   
       16 . The method of  claim 15 , wherein the step of mounting the target is performed by affixing a label to said one overscan region, and the step of printing the areas of different light reflectivity on the label.  
   
   
       17 . The method of  claim 15 , wherein the step of mounting the target is performed by molding markings into said one overscan region.  
   
   
       18 . The method of  claim 11 , wherein the detecting step includes the steps of generating an over-power signal having a magnitude indicative of the output power of the laser beam, comparing the magnitude of the over-power signal with a reference value, and generating a control signal when the magnitude of the over-power signal exceeds the reference value.  
   
   
       19 . The method of  claim 18 , wherein the detecting step includes the step of differentiating the over-power signal to obtain a differentiated signal having peaks, and wherein the comparing step is performed by comparing the peaks to the reference value, and wherein the generating step is performed by generating the control signal when the peaks exceed the reference value.  
   
   
       20 . The method of  claim 18 , wherein the deenergizing step is performed by opening a switch electronically connected between a power source and the laser upon generation of the control signal.